Lag fuse



June 19, 19 51 L. N. BAENZIGER LAG FUSE Filed Aug. 24, 1950 r m an MA 3% n Ifiz M Patented June 19, 1951 LAG FUSE Leonard N. Baenziger, Pawtucket, R. I., assignor to Royal Electric Company, Inc., Pawtucket, B. 1., a corporation of Rhode Island Application August 24, 1950, Serial No. 181,243

2 Claims.

This invention relates to improvements in plug type fuses commonly known as lag fuses, adapted for use in the circuits of electrical appliances and designed to accommodate a quick surge of current when the switch in the appliance circuit is turned on, Without blowing because of the quick surge of current which temporarily overloads the circuit.

The principal purpose of the invention is to provide a plug fuse of this type which is simple and economical to manufacture and assemble, durable and efficient in use and capable of carrying normal currents and temporary overloads without interrupting the circuit, while causing interruption of the circuit under sustained over loads or short circuits.

More particularly, it is an object of this invention to provide a lag fuse having body and shell portions of substantially conventional construction, equipped with a fusible strip having solder-filled. coils on opposite sides of the fusible neck or link of the strip, whereby the solder pockets absorb the excess heat of a quick current surge of temporary overload such as occurs when the circuit to an electric appliance is first turned on, so that the circuit is not broken unless the overload is sustained for a predetermined period of time.

A recommended embodiment of the invention is shown in the accompanying drawings, in which:

Fig. 1 is a plan view of the improved fuse, partly broken away and in section, taken on line |l of Fig. 2;

Fig. 2 is a diametric section on line 2-2 of Figure 1;

Fig. 3 is a composite view showing, in plan and in edge elevation, a fusible metal strip in fiat form, prior to the coiling of the strip and the incorporation of the solder pockets; and

Fig. 4 is an enlarged, fragmentary edge elevation, partly in section, showing the fusible link and solder pockets in the coils of the fused strip.

In the form chosen for the purpose of illustration, the improved lag fuse comprises a substantially conventional body i I of insulating material, a conventional transparent top member or cover [2, of glass or other suitable material, and a conventional threaded metal shell it which holds the body and cover in assembled relation and provides means for screwing the plug fuse into a conventional socket, in which the base terminal I l of the fuse and the shell it constitute conductors when the circuit is open. The aforesaid elements are common to various types of plug fuses, and the structural details of these elements are not material to the present invention and may be modified as desired to suit particular purposes.

In accordance with this invention, the fuse strip normally incorporated in such plug type fuse performs the general function of conventional fuse strips but is of novel construction most economically and efficiently to perform the functions and purposes above described. The strip l5 consists of zinc or other fusible metal and is of such a length to be incorporated in the fuse plug so that one end is electrically connected to the screw shell I3 as at It and the other end is electrically connected as at H to the base terminal it, with the central portion of the strip extending across the top of the insulating body I l above the customary paper disc l8. The strip l5 has a reduced central neck fusible link portion H9. The electrical connections l6 and I1 may be achieved by soldering the parts together in accordance with ordinary practice.

On opposite sides of the link IS, the metal strip is coiled upon itself at 20, as best shown in Fig. 4, and the openings in the respective coils are filled with molten solder 2i which, upon hardening, forms solder pockets in each of the coils 29 and retains said coils against displacement When the fusible strip [5 is incorporated in the plug as shown in Figs. 1 and 2, with the solder pockets disposed above the disc It on top of the hollow insulating body I I. As previously indicated, these solder pockets absorb the excess heat of a quick current surge and prevent the breaking of the fuse at the link it under a temporary overload of the circuit. If, however, such overload is sustained for a predetermined time period, because of a short in the circuit, or for other reasons, the fusible link will melt and the circuit will be interrupted before any damage to the electrical appliance results.

ihe fusible strip of a lag fuse constructed as above described avoids the necessity for using special links or springs, such as employed in certain previous types of lag fuses, which are complicated to manufacture and assemble and likely to get out of order in use. The solder-pocketed strip is easy to manufacture, compact in form, and may be assembled with the other elements of the fuse plug without introducing additional parts or special connections.

1. A lag fuse comprising a flat metal strip having a fusible link of reduced width intermediate its ends, said flat strip being coiled upon itself on opposite sides of said link, said coils having 2,557,587 I 3 4 transverse pockets therein and said pockets con- REFERENCES CITED taining solder.

A p g ype lag fuse comprising a body of The following references are of record in the insulating material, a cover of transparent infile of this patent:

sulating material, a threaded shell partially en- 5 UNITED ST PATENTS closing said body and cover and holding the same in assembled relation, a terminal in the base of gg dName F 2 said body, and a flat strip of fusible metal having 3 4252 g g' 3 1930 its respective ends connected to said shell and said terminal and having an intermediate por- 10 FOREIGN PATENTS tion extending across the top of said body, said Number Country Date intermediate portion having a reduced neck con- 156 249 Switzerland Oct. 1 1932 stituting a fusible link, the flat metal strip being 197979 Switzerland Dec 1938 a coiled upon itself on opposite sides of said 1ink 4623577 Great Britaifi 1937 to provide pockets in the coils, said pockets con- 15 653:113 Germany 1937 taining hardened solder.

LEONARD N. BAENZIGER. i 

